A point to remember in all this.....as I have pointed out many times over the years to people who speak before they think....these things are far more likely to happen in America simply because of the population size for starters.
We have had couple in the UK, that I can recal...and a few in Europe over the years but there are 315 million people in America.....so simple maths tell us these attacks are more likely there than in say the Uk, where 64 million people live.